1. Field of the Invention
The present invention relates generally to annulus pressure responsive downhole tools utilizing a compressible liquid spring.
2. Description of the Prior Art
The prior art includes a number of downhole tools, such as flow tester valves and circulating valves, which are designed to operate in response to changes in pressure in a well annulus between a tool string and a well casing. Typically, these tools include a differential area piston, which may generally be referred to as a power piston, having one side communicated with well annulus pressure and having another side communicated with a compressible fluid spring chamber.
The compressible fluid spring chamber typically has been filled either with a compressible gas such as nitrogen or a compressible liquid such as silicone oil.
When well annulus pressure is increased to move the power piston of the tool, the fluid in the spring chamber is compressed. Upon decreasing the well annulus pressure, the compressed fluid in the spring chamber expands to aid in returning the power piston to its original position.
Typical examples of prior art tools utilizing compressible nitrogen spring chambers are seen in U.S. Pat. Nos. 4,422,506; 4,429,748; 4,489,786; and 4,515,219, all to Beck and all assigned to the assignee of the present invention.
Two prior art circulating valves utilizing compressible silicone oil spring chambers are shown in U.S. Pat. Nos. 4,109,724 to Barrington and 4,109,725 to Williamson et al., both assigned to the assignee of the present invention.
Two prior art tester valves utilizing silicone spring chambers are shown in U.S. Pat. Nos. 4,444,268 and 4,448,254, both to Barrington and both assigned to the assignee of the present invention.
The present invention relates to a particular design for a downhole tool using a compressible liquid spring chamber, preferably using silicone oil, which may be utilized to convert a typical prior art tool originally designed for use with a compressible nitrogen spring chamber to a compressible liquid spring chamber design.
Also provided are improvements generally applicable to compressible liquid spring chamber tools with regard to the use of a relief valve to allow for expansion of the compressible liquid upon heating as the tool is lowered into a well.